Receptor and biological response to estriol in the fetal uterus of guinea pig

The binding of 3H-estriol was examined in the fetal uterus of guinea pig. The physico-chemical characteristics of the binding of 3H-estriol to macromolecules are similar to the typical receptor protein for estrogens. Different estrogens (estriol, estradiol, estrone and diethylstilbestrol) compete with this binding but progesterone and testosterone have no effect. The binding affinity has a Kd of 5.5 +/- 1.6 +/- 10(-10) M. By ultracentrifugation in sucrose gradient, two specific components with sedimentation coefficients of 8 and 4S are found. Competition studies suggest that the same specific binding sites may be present for estriol (E3) and for estradiol. The s.c. administration of E3 to the pregnant guinea pig (1 mg/day per kg body weight for 3 days) provokes two biological responses in the fetal uterus: a uterothopic effect and a significant increase in the progesterone receptor. The increase in the fetal uterine weight is 50-70% in relation to the non-treated animals and the progesterone receptor concentration is 10-14 times higher than in the control animals. These effects are similar (or slightly higher) than in animals primed with equimolecular quantities of estradiol. In contrast, single daily injections of E3 to newborn guinea pig, results only in weak uterotrophic activity. It is concluded that estriol is capable of causing a biological response in the uterus during intra-uterine life.

Estrogen and progestin regulation of the progesterone receptor concentration in human endometrium

The concentration of the progesterone receptor (PR), both cytosol and nuclear, has been measured in the endometrium of 31 normal menstruating women during the 2 phases of their menstrual cycle and compared with the plasma 17 beta-estradiol and progesterone concentrations. There was no relationship between PR concentrations and the plasma steroid levels when the 2 phases of the cycle were considered; however, a statistically significant correlation (r = 0.70; P less than 0.005) was observed between PR concentration and plasma 17 beta-estradiol when only the follicular phase was considered. PR was then measured in the endometrium of 14 postmenopausal patients treated with ethinylestradiol at increasing doses with or without association of chlormadinone acetate. Ethinylestradiol was shown to increase PR concentration (P less than 0.05), and chlormadinone acetate was found to prevent this increase. These data suggest that in humans, as in other mammalian species, the endometrial PR concentration is under estrogen and progestin control.

Inhibition of estrous behavior by progesterone in rats: role of neural estrogen and progestin receptors

Sexual receptivity can be induced in ovariectomized rats with sequential injections of 17 beta-estradiol-3-benzoate (EB; 2 micrograms sc) and progesterone given 24 h apart. If a high dose of progesterone is used, estrous behavior is followed by a period during which sexual receptivity cannot be reinduced with a second progesterone injection (sequential inhibition). We have examined the effects of a hormone treatment which causes a sequential inhibition on levels of estrogen and progestin receptors in the hypothalamus-preoptic area-septum of ovariectomized rats. In a preliminary experiment, a single injection of 2 micrograms EB caused a significant increase in the concentration of brain cell nuclear estrogen receptors, Peak levels were seen at 12-24 h and remained significantly elevated as long as 72 h after EB. In a second experiment, we found that 48 h after EB, brain cytoplasmic estrogen receptors were significantly depressed and nuclear estrogen receptors were significantly elevated. However, a single progesterone injection (5 mg, sc) 24 h after EB had no significant effect on either cytoplasmic or nuclear estrogen receptor levels. Forty-eight hours after EB, brain cytoplasmic progestin receptors were significantly elevated compared with oil-injected controls. In a third experiment, progesterone (5 mg, sc) given 24 h after EB reduced neural cytoplasmic progestin receptors to levels significantly below those of oil-injected controls at 48 h. These results are consistent with the suggestion that progesterone does not interact with neural estrogen receptors to inhibit lordosis in rats. Rather, we suggest that progesterone may induce a behavioral refractoriness to subsequent progesterone treatments, at least in part, by reducing the concentration of neural cytoplasmic progestin receptors.

Progesterone "receptor" in rat ovary

A soluble thermolabile protein with many characteristics of a progesterone receptor has been identified in ovaries of estrogen-stimulated, hypophysectomized, immature female rats. A potent synthetic progestin R5020 (17,21-dimethyl-19-nor-pregna-4, 9-diene-3, 20-dione) and a progestin-receptor complex stabilizer (glycerol) were employed. After the incubation of [3H]R5020 with ovarian cytosol, fractionation of a Sephadex G-200 column revealed a peak of radioactivity which eluted with the void volume. This peak, which represented saturable binding, disappeared after heating (37 C for 20 min) and trypsinization. In the absence of glycerol, binding decreased by 84%. Scatchard analysis of the binding curve showed the R5020 binding to be of moderately high affinity (Kd 4 nM), with 232 fmol binding sites/mg cytosol protein. Binding site number rose linearly with increasing cytosol protein concentration. The relative abilities of various steroids to inhibit [3H]R5020 Binding were: R5020 greater than progesterone greater than estradiol greater than testosterone greater than cortisol greater than diethylstilbestrol. [3H]R5020 was not metabolized and did not bind specifically to serum. In summary, we have identified a protein with characteristics of a progesterone receptor in the cytoplasmic fraction of ovarian tissue.

Effect of oestradiol on progesterone receptors in normal mammary glands and its relationship with lactation

Mammary glands of lactating mice, either intact or ovariectomized, do not contain detectable amounts of progesterone receptors and this lack of receptors persists also in tissues of animals treated with oestradiol. In contrast with lactators, mammary glands of virgin mice contain progesterone receptors whose amounts are augmented by oestradiol administration.